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engine mods to a O.S. .21 xm outboard

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engine mods to a O.S. .21 xm outboard

Old 04-02-2006, 08:52 PM
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lelandhild
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Default engine mods to a O.S. .21 xm outboard

Is there any engine mods I can do to a os .21 xm outboard by myself without spending any money.any help would be appreciated.
Old 04-02-2006, 09:19 PM
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oldlugs
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Default RE: engine mods to a O.S. .21 xm outboard

Yes. I'd do a basic port clean-up. You can use a Dremel if you have one, but a set of needle files and some 320 grit wet-dry paper are all you need. Look here to get some idea of what you're doing: [link=http://home.earthlink.net/~ob_nut2/id24.html]simple port mods[/link] You basically just want to round out and blend the edges leading into the ports so that flow is increased. Don't cut into the inside of the sleeve without doing your homework, just clean up the outside. Stare at the sleeve for a while, and use some common sense. You can also do some piston "skirting", but you don't want to cut it on the exhaust port side. Do some research, and you'll learn plenty...
Old 04-02-2006, 09:57 PM
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Ron Olson
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Default RE: engine mods to a O.S. .21 xm outboard

If you don't know what you're doing, you are better off not messing around with the piston and sleeve. Work on setup and props.
Here's a perfect example of what I'm typing about. This past weekend in Huntsville, Alabama the stock OB tunnel record was broken with 60 MPH passes!!! This is a dead stock, out of the box OS .21 . 99% of the modified engines can't do this speed! Setup, setup, setup is the key. Play with head shims, glow plugs, fuel, carb mixture, props and every part of your boat to get the most out of your boat.
Old 04-03-2006, 01:26 AM
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oldlugs
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Default RE: engine mods to a O.S. .21 xm outboard

Ron's right of course... I like to play with engines too much. I just can't leave one stock...
Old 04-03-2006, 04:02 PM
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lelandhild
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Default RE: engine mods to a O.S. .21 xm outboard

thanks for the help guys. 60 mph is pretty fast. I was wondering what a head shim was. and what a good tuned pipe was for an os .21 outboard. also how do you actually tune a tuned pipe.
Old 04-04-2006, 10:11 AM
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ob nut
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Default RE: engine mods to a O.S. .21 xm outboard

There is only one way to "tune" a tuned pipe. To get the most out of the motor, the pipe length have to matched. To do this, move the pipe in or out, shorting or lengthening the pipe. One must play with the length to suit the boat, motor and prop.

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